Panoramiclike dental arch x-ray apparatus

ABSTRACT

The obtention of a panoramiclike radiograph of the upper and lower dental arches composed from overlapping exposures of X-rays directed successively at different angles from the back of the patient&#39;&#39;s head towards a forwardly disposed extra-oral film supported on a vertically adjustable framework assembly which includes a laterally movable holder for the film as well as a fixed reference plate for positioning within the patient&#39;&#39;s mouth at the occlusal plane between the upper and lower dental arches. The plate within the patient&#39;&#39;s mouth constitutes a reliable stabilizing device against movement during exposure and presents a constant plane of reference in successive radiographs by the dentist for comparisons of progress or growth. The framework assembly also comprises a fixator or support for an X-ray unit which may be shifted angularly and rectilinearly and is indexed at predetermined positions to make possible a rapid setting of the components while the patient remains fixed, for obtaining radiographs of consistently excellent characteristics despite variations in the shape and size of the patient&#39;&#39;s head and dental arches.

United States Patent Martin L. Schulman, Washington, DC.

[72] Inventors 20016; Thomas M. Howard, Jr., Clarksville,

211 App]. No. 823,121

[22] Filed May 8, 1969 [45] Patented Nov. 2, 1971 [73] Assignee Dental Corporation of America Rockville, Md.

[54] PANORAMICLIKE DENTAL ARCH X-RAY [56] References Cited UNITED STATES PATENTS 2,798,958 7/1957 Hudson et al 250/61.5 2,829,263 4/1958 Butler 250/65 Primary Examiner-James W. Lawrence Assistant ExaminerA. L. Birch AttorneySam uel Lebowitz ABSTRACT: The obtention of a panoramiclike radiograph of the upper and lower dental arches composed from overlapping exposures of X-rays directed successively at different angles from the back of the patients head towards a forwardly disposed extra-oral film supported on a vertically adjustable framework assembly which includes a laterally movable holder for the film as well as a fixed reference plate for positioning within the patients mouth at the occlusal plane between the upper and lower dental arches. The plate within the patient's mouth constitutes a reliable stabilizing device against movement during exposure and presents a constant plane of reference in successive radiographs by the dentist for comparisons of progress or growth. The framework assembly also comprises a fixator or support for an X-ray unit which may be shifted angularly and rectilinearly and is indexed at predetermined positions to make possible a rapid setting of the components while the patient remains fixed, for obtaining radiographs of consistently excellent characteristics despite variations in the shape and size of the patients head and dental arches.

PATENTEDHOV 2 IBII SHEEIEUF 4 This invention relates to an .apparatus for producing a panoramiclike radiograph of the dental arches by taking a series of separate adjacent X-rayjradiographs in coordinated relation on a unitary photographic plate, by successively directly a beam of X-rays, issuing from a nose cone of an X- ray unit, at diflerent angles towards the open end of the dental arches at the approximate level of the occlusal plane, to obtain adjacent and slightly overlapping exposures of the'posterior left, anterior left, anterior right and posterior right portions of the dental arches, while the patient remains in stationary position.

It is the-object of the present invention to provide a rugged and reliable installation to obtain radiographs of the dental arches which is much simpler and therefore much less costly than those presently known in the art, and as exemplifiedby those illustrated in U.-S. Pat. Nos. 2,264,410, Dec. 2, 1941, 2,684,446, July 20, 1954, and 3,045,l'l8, July 17, 1962.

It is a further object of the invention to provide apanoramiclike radiograph of the dental arches characterized by maximurii clarity, minimal distortion, and the least interference from the extraneous bone structures of the body.

The invention proceeds upon the principle of positioning the patient comfortably and immobilizing the dental arches by inserting a positioning plate within the mouth of the patient to fix the occlusal plane between the arches. An orbiting fixator device for supporting an X-ray unit is mounted on the framework assembly which orients the positioning plate in'the patient's mouth, so that the X-ray unit may be shifted relatively thereto to predetermined positions for obtaining the desired angulated directions of the-X-ray beam through the different portions of the dental arches onto the photographic plate which is disposed in front of the patient, and which is shiftable to different positions corresponding to the respective positions of the X-ray beam to obtain thereon optimum exposures of the portions of the dental arches.

Particularly advantageous results are obtained by the instant invention by lowering the X-ray unit in the course of making the anterior exposures and simultaneously angling the beam of X-rays upwardly to an angle of approximately 5;in order to photograph the upper central root structures without interference from the bone structure of the upper palate. Furthermore, the exposures of these anterior portions are made in directions at angles ranging from 9 to 19 from the longitudinal axis of the dental arches, and preferably 14. These equal angular displacements on each side of said axis incidental to the exposure of the anterior portions of the dental arches bypass the human spine and thus avoid the intense X- ray scatter" and interference which is caused by the bone structure of the spinal column.

The orbiting fixator of the X-ray unit is not only indexed for the exposure of the anterior portions of the dental arches, but is also indexed with positive stops when the posterior exposures at the left and right of the mouth are made, at angles ranging from 37 to 47 relative to the longitudinal axis, and preferably 41 A.

The photographic plate holder which is movable in front of the patient is arch-shaped in horizontal cross section and is indexed positively to the proper position at the time the anterior exposures are registered, as well as when the posterior exposures are made, in which case the holder and the photographic plate closely abut the sides of the patients head. The close proximity of the photographic plate to the arches gives rise to clear radiographs with minimum'distortion. The fixed indexing positions of the photographic plate holder and the orbiting fixator, in conjunction with the fixed positioning plate in the mouth of the patient assure identical positional exposures at different times so that the dentist may compare easily and reliably the progress of the work being done or the growth of the patient.

Other objects and purposes will appear from the detailed description of the invention following hereinafter taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view showing the general layout of the installation with a patient seated in position for taking the radiographs;

FIG. 2 is a rear view of the lower extremity of the fixator device for supporting the X-ray .unit in a raised-substantially horizontal position;

FIG. 3 is a'vertical sectional view along line33 of FIG. 2 with the dotted line representingthe fixator in a'lowered and tilted position;

FIG.'4 is a plan view of the framework assembly mounted on a vertical support with the 'fixator in position for exposing the anterior right portion of the dental arches, and with the other indexed positions of the fixator device shown in dotted lines;

FIG. 5.is a side elevation of the framework assembly with the orbiting fixator in position to expose the anterior right portion of the dental arch;

FIG. 6 is a vertical sectional view, with parts broken away, along line 66 of FIG. 4;

FIG. 7 is a vertical sectional view,'similar toFIG. 6, illustrating a variant-embodiment;

FIG. 8 is a horizontal sectional view along line 8-8 of FIG.

FIG. 9 is a front elevation of the photographic cassette holder with the positioning occlusal plate forwardly thereof, and the dotted lines representing other positions of said cassette holder;

FIG. 10 is a vertical sectional view along line l 0-1 0 of FIG. 8.

In the drawings is shown a preferred embodiment of the invention. The'vertical support 1 is mounted adjacent to a wall W through the intermediary of spaced wall brackets'B. This vertical support may be of channeled configuration, and a seat 2, suitably braced by the diagonal strut 3, serves as a seat for the patient facing the sup'portand wall; Ofcourse, the patient mayassume a standing position, if desired, in which case the seat is removed-from the device.

The primary component of the invention, consisting of a framework assembly 10 is mounted on the vertical support 1 at an adjustable level. This assembly consists of a vertical plate 11, a transverse .plate- 12, at the upper end of plate 11,1which extendsover the head of the patient, and a horizontal plate 13 at the lower end of vertical plate 11 which may be detachably connected thereat by means of a bolt and wing nut 13'. The positioning plate 18, which is adapted to be inserted between the dental arches of the patient to define the occlusalplane extends upwardly from plate 13. It is understood that the distance between the seat 2 and the positioning plate 18 varies in dependence upon the physical requirements of the patient. As stated above, the patient may be in standing position in which case the positioning plate is inserted in the mouth of the patient at a level depending on the height of the patient. The positioning plate I 8 extends transversely from a supporting member 18', the lower end of which is affixed to horizontal plate 13. The latter may be removed for sterilization and cleaning by detaching the wing bolt 13' from the lower end of plate 11. The positioning plate and its support are preferably formed of a material which is at least translucent to X-rays,'

such as Lucite.

The purpose of the plate 18 is to immobilize the patient from any movement when biting it while exposure is being made and to provide a parallel plane for the X-ray procedure which, in the two posterior exposures, will result in a more nearly true tooth size and tooth relationship than any other basis for patient orientation. Said device further provides a reattainable basis of patient orientation for future exposures to determine changes in patient anatomy from series to series of exposures.

The forward face of vertical plate 11, in addition, isprovided at its lower end with track guides 16 and 17 for the purpose of guiding a photographic cassette holder 52 for lateral movement as explained in greater detail below.

beam of X-rays from its nose cone through the open ends of the dental arches for exposure on a photographic plate within a flexible cassette 62 which is retained on holder 51.

The cassette holder 51 which is shown clearly in FIGS. 4, 8, 9 and 10, is of arch-shaped construction in horizontal section and is provided with an upwardly extending lip 60 along the bottom margin thereof for retention of a photographic cassette 62 and the covering shields therefor comprised by four sectional plates 63, 65, 67 and 69 which are successively removed as the exposures are made of the posterior left, anterior left, anterior right and posterior right portions of the dental arches. These shielding plates are removed in succession with the aid of extension tabs (FIG. 9), as the X-ray unit is directed along the axes PL, AL, AR and PR, which axes are indicated in FIG. 8 respectively. The cassette holder 51 is provided with a flexible plastic lining 61 containing lead at the front face thereof and similar X-ray impermeable linings 64 are affixed to the rear faces of the'sectional plates 63, 65, 67 and 69. The end plates 63 and 69 are additionally provided with protective lips 63:: and 69e to protect the ends of the cassette against the admission of X-rays thereto at these edges.

it should be noted that when the anterior exposures are made, and the nose cone is positioned along the axes AL and AR, the spinal column S of the patient is clear of the X-ray beam which serves to avoid the intense X-ray scatter and interference which is caused by the bone structure of the spine. Significantly improved results are attained by adjusting the beam of the X-ray in another direction, namely, by lowering the nose cone for a slight extent, of the order of 1 inch, and at the same time tilting the nose cone upwardly at an angle of approximately 5, which serves to photograph the upper central root structures of the upper dental arch without interference from the bone structure of the upper palate.

Also it has been determined that the occlusal plane, if tilted in an upward direction, serves to contribute to the obtention of clearer images of the root structures in the anterior area. For this reason, the positioning plate is shown directed upwardly in the mouth of the patient to attain this result (FIG. 5). This upward tilt may amount toapproximately 8.

The separate successive radiographs which are directed along the four axes shown in FlG. 8 overlap to some degree but they are all exposed on a unitary film. Thus, for example, the posterior left exposure includes the third tooth which is common to the anterior left exposure and the latter may include the first and part of the second tooth of the anterior right exposure. Therefore it is important that these axes of the X-ray beam be fixed for all exposures of the different portions of the dental arches so that comparisons can be made from time to time with the assurance that the radiographs were made under uniform conditions. To attain this uniformity, the axes AL and AR are displaced from the longitudinal axis of the positioning plate and dental arches 9 to 19 and preferably 14, on each side of the longitudinal axis. Similarly, the axes PL and PR are displaced 37 to 47 and preferably 41%" from this longitudinal axis. Suitable indexing means is provided on the installation to uniformly set the X-ray unit relative to the patient to attain these fixed angulations.

As shown in FIG. 8 with the nose cone in solid lines in the course of making the exposure of the anterior right portion of the dental arch, the laterally shiftable plate holder 52, to which is afiixed the cassette retainer 51 by means of screws 53, is moved in position to expose the right central portion of the photographic negative, and suitable indexing means is provided to fix the cassette retainer in the course of making this exposure. When the posterior right exposure is to be made, the photographic plate holder is shifted further until the arcuate-shaped plate holder is positioned on the side of the face of the patient which results in clear radiographs with minimal distortion.

The plate holder is shifted in the reverse direction in the course of making the anterior left exposure and ultimately the posterior left exposure when the nose cone is positioned along axes AL and PL respectively.

The drawings illustrate one preferred embodiment for executing the procedures described above and particularly the positioning of the nose cone of the X-ray unit in the course of making the anterior exposures as well as indexing the fixator device for the X-ray unit in the course of making all four exposures.

The X-ray unit U which may be mounted on a wall, or which may be of the portable type, is designed to be supported in a stirrup member 30 which is disposed at the lower extremity of a downwardly extending member 25 which is shiftably mounted on a bar 20 having the forward end thereof mounted for pivotal movement to the horizontal plate 12 of the subframe assembly. The pivot member 21 permits rotary movement of the fixator behind the patient's head, and suitable stops may be provided in the arcuate path of its movement to fix the direction of the nose cone at the predetermined angles indicated above, for example, 14 on each side of the longitudinal axis for the purpose of making the anterior exposures, and 42% on each side of the midsagittal plane of the patient for the purpose of making the posterior exposures. These stops may be afforded by a cylindrical pin in a corresponding opening at the center of the forward part of bar 20 dropping into selective engagement with any one of four cylindrical openings in the plate 12, displaced at 14 and 42% from the longitudinal axis of the plate on each side thereof.

A preferred embodiment for obtaining this indexing is shown in FIG. 6, wherein the plate 12 is provided with a plu--- rality of dimples 45 disposed at these critical angles of 14 and 42%" on each side of the longitudinal axis, which are designed to receive a ball detent 46 which is pressed by spring 47 and screw bolt 49 disposed centrally at the forward end of the movable bar 20. This arrangement permits the movement of the fixator device from one position to the other by the application of a force sufficient to cam out the ball detent from its seating dimple. Another alternative arrangement is shown in FIG. 7 wherein a spring-pressed plunger 79, seated selectively in one of four apertures 75 is lifted positively to shift the fixator device from one position to another.

The downwardly extending member 25 in FIG. 5 is provided with a sleeve 26 at the upper end thereof which is slidable on the bar 20 and which may be fastened by the screw bolt 27 to control the setting of the nose cone in a longitudinal direction with respect to the head H of the patient.

When the anterior exposures are to be made, the stirrup 30 is designated to be dropped to a slight extent, and this construction is shown in FIGS. 2, 3 and 5 of the drawings. The stirrup 30 with the circular opening 31 at the lower end thereof for embracing the X-ray unit constitutes the lower one of two interconnected plate members 30 and 32 which are integrated by screw bolt 33. The upper portion of the upper plat member 32 is formed as a sleeve 34 which embraces loosely the lower end of member 25 which is provided with lateral rectangular notches 28, 28 having a predetermined height in excess of that of sleeve 34, for example, 1 inch. A threaded fastening bolt 35 extends through a threaded opening in sleeve 32 and clamps the sleeve to the outer face of member 25 in the raised position of the sleeve (FIG. 2). The loosening of the bolt 35 permits the sleeve to drop said 1 inch to the lower edges of the notches 28, 28'. The bottom extremity of the outer face of member 25 is formed as a plane 29 inclined to the vertical, for example, 5, so that when screw bolt 35 is tightened against this inclined surface, the stirrup member is tilted upwardly a corresponding angular amount. The inner face of member 25 is notched at 36 to accommodate the upper edge of the inner portion of sleeve 34 in'the tilted position of the stirrup which is indicated in dotted lines in FIG. 3.

This stabilizes the positioning of the fixator support for the X- ray unit in both its raised and lowered positions.

A spring-pressed ball detent 56 (FIG. 8) is locked within the vertical plate 11 at the level of the sliding plate holder 52, for selective cooperation with depressions or vertical channels 57, 57 of suitable contour in the forward faceof the, holder 52 and displaced from each other a distance to effect thejndexing of the holder at each anterior portion of the cassette retainer 51.

The indexing means for the shiftable cassette retainer 51 for the posterior exposures is afforded by sliding the arch-shaped cassette retainer into close abutting contact with the sideof the face of the patient preparatory to lifting the respective covering shielding plates 63 or 69. lnno case, however, will the lateral movement of the cassette holder 51 go beyond the.

point of engagement of the side of the occlusal plate support 18 and the cassette holder lip at 60';

The panoramiclike radiograph accordance with the, invention may be made in a matter of minutes by the following procedure;

The patient may be seated and the framework assembly is adjusted to a level which brings the positioning plate 18 to the level of the mouth of the patient. He is requested to bite onthe plate which may be covered on both'the upper and lower faces with thin wax laminates to afford greater comfort while the patient remains in an immobilized position. The patients nose-is. brought into contact with the vertical median of the-shiftable plate holder when centered to assure a close setting of the-patient to the photographic plate when in a central position.

Thereafter, the slide 52 is shifted'to its'extreme position to the right, to bring the cassette holder into contact with the left side of the patients face. The fixator device is moved in a horizontal plane to axis PL, covering shield 63 is removed, and the X-ray energy is directed through the posterior left portion of the dental arches to expose that portion of the film, which is then covered with shield 63. I

Slide 52 is then shifted to the left until ball detent 56 engages groove 57' to bring the left central portion of the film in front of the anterior left portion of the dental arches. The fiXa-. tor device is shifted to axis AL, the'stirrup supporting the X- ray unit isdropped and tilted upwardly, which is followed by; the lifting of covering shield 65 and the shooting of the beam of X-rays through the anterior left portion of the dental arches.

The covering shield 65 is replaced. The slide 52 is moved to the left and indexed at 56, 57 as shown in FIG. 8, to bring the right central portion of the film in :front of the right anterior position of the dental arches. The fixator device is moved to axis AR, covering shield 67 is removed, and the X-ray unit is energized to expose the last-mentioned portion of the dental arches which is followed by the replacement of covering shield 67.

Finally, the slide 52 is moved to its limiting position to the left to bring the cassette retainer into contact with the right side of the face of the patient, fixator device is moved to axis PR. The stirrup is raised and clamped in raised position, slide 69 is removed, the X-ray unit is energized, followed. by the replacement of slide 69 which results in the exposure of the posterior right portion of the dental arches and the completion of the panoramiclike radiograph.

This is all done in a few minutes, while the patient remains in his original stationary position.

We claim:

1. In an apparatus for producing a radiograph of the dental arches by taking a series of at least four separate overlapping successive X-ray radiographs in coordinated relation on a unitary photographic plate,

a. a frame comprising a vertical member adapted to be disposed in front of a patient with a horizontal member extending transversely therefrom above the head of the patient,

b. a plate holder assembly for said photographic plate mounted on said vertical member,

c. means for fixing the level of said assembly on said frame in correspondence to the level of the patients mouth,

d. a positioning plate mounted on said assembly and adapted to be inserted at the occlusal plane between the upper and lower dental arches within the mouth of the patient in fixed position facing said frame,

e. a fixator device including a support for a sourceof X-rays pivotally mounted on said horizontal memberfor movement about a single axis medially of said positioning plate and dental arches and above the posteriorportion of the upper-palate beyond the open end of .the dental arches, said source of. X-rays adapted to execute incremental discontinuous movements in an arcuate path behind the head of the patient and to direct the X-rays projected from said source at the approximate leyel of said occlusal plane from-behind the patient towardsseparate sectionalized portions of the photographic plate in front of the patient,

f. guide means on said-plate holder assembly for permitting incrementallateral movement of said photographic plate in a horizontal direction relative to said fixed positioning plate, and

g. means for manually shifting the angular positionof said fixator device relative to said fixedpositioning plate in said successive increments, to project the X-rays emanating from said source to said sectionalized portions of .the photographic plate which are adapted to be successively exposed thereto.

2; An apparatus as set forth in claim 1, wherein said plate holder assembly is generally arch-shaped, in horizontal cross section for supporting the photographic plate vertically in an arch corresponding to the assembly, for recording thereon, in

adjacent relation, the posterior left, theanterior left, the an-.. terior right and posterior right exposures of the dental arches,

saidexposuresbeing in slightly overlapping relation.

3. An apparatus as set forth in claim 2, wherein said archshaped plate holder assembly has a vertical median adapted to be shifted laterally relative to the midsagittal plane of the dental arches during the exposure of the anterior and posterior portions of the latter on each side of said axis.

4. An apparatus as set forth in claim 2, wherein said plate holder assembly is adapted to be shifted. to its positions as close to the areas being radiographed as possible by indexing the lateral movement of the assembly to expose the sectionalizedportions of the photographic plate adjacent to therespective position of the head of the patient when the respective exposures are made.

5. An apparatus as set forth in claim 1, wherein said plate holder assembly comprises supporting means for said positioning plate extending upwardly from the lower end of said assembly, said positioning plate and supporting means being formed of radioluscent material.

6. An apparatus as set forth in claim 1, wherein said fixator device comprises a. an auxiliary bar having the forward part thereof pivotally connected to said horizontal member of said frame for movement in a horizontal plane,

b. a downwardly extending member on the rearward part of said auxiliary bar for supporting the source of X-rays, and

c. cooperating detent means on said auxiliary bar and horizontal member to fix the angular relation therebetween at predetermined positions angled relative to the midsagittal plane of the patient.

7. An apparatus as set forth in claim 6, wherein said cooperating detent means comprises detent elements disposed at equal angles ranging from 9' to 19 from said midsagittal plane, to permit substantial avoidance of the spinal column of the patient by the beam of X-rays adapted to emanate from said X-ray source when the anterior exposures on the left and right are made.

8. An apparatus as set forth in claim 7, wherein said detent elements are disposed at an angle of approximately 14 on each side of said midsagittal plane.

9. An apparatus as set forth in claim 6, including means on said downwardly extending member for lowering the X-ray source slightly below the occlusal plane and tilting said source upwardly for a limited angular extent in the course of exposing the central portions of the photographic plate on each side of the vertical median thereof whereby the upper central root structures of the upper dental arch may be radiographed without interference from the bone structure of the upper palate.

10. An apparatus as set forth in claim 9, wherein said mounting means for the X-ray source is adapted to lower said source approximately one inch and to tilt the source upwardly approximately 11. An apparatus as set forth in claim 9, wherein said plate holder assembly for supporting the photographic plate is archshaped in horizontal cross section for supporting the photographic plate vertically in an arch corresponding to the assembly, and position-indexing means on said assembly for locating the fixed sectionalized positions of the photographic plate during the successive incremental exposures of the dental arches.

12. An apparatus as set forth in claim 7, wherein said cooperating detent means comprises detent elements disposed at equal angles ranging from 37 to 47 from said midsagittal left and right sides of the dental arches are made.

13. An apparatus as set forth in claim 6, wherein said cooperating detent means comprises detent elements disposed at equal angles ranging from 37 to 47 from said midsagittal plane, to fix the trajectory of the beam of X-rays adapted to emanate from said source when the posterior exposures of the left and right sides of the dental arches are made.

14. An apparatus as set forth in claim 13, wherein said detent elements are disposed at an angle of approximately 42% on each side of said midsagittal plane 15. An apparatus as set forth in claim 6, including means at the junction of said auxiliary bar and downwardly extending member for shifting longitudinally the radial position of the X- ray source relative to the patient.

16. An apparatus as set forth in claim 1, wherein said positioning plate adapted to be positioned in the mouth of the patient is arch-shaped and is canted upwardly from the anterior of the mouth to tilt the occlusal plane accordingly.

17. An apparatus as set forth in claim 16, wherein the canting angle of the positioning plate is approximately 8. 

1. In an apparatus for producing a radiograph of the dental arches by taking a series of at least four separate overlapping successive X-ray radiographs in coordinated relation on a unitary photographic plate, a. a frame comprising a vertical member adapted to be disposed in front of a patient with a horizontal member extending transversely therefrom above the head of the patient, b. a plate holder assembly for said photographic plate mounted on said vertical member, c. means for fixing the level of said assembly on said frame in correspondence to the level of the patient''s mouth, d. a positioning plate mounted on said assembly and adapted to be inserted at the occlusal plane between the upper and lower dental arches within the mouth of the patient in fixed position facing said frame, e. a fixator device including a support for a source of X-rays pivotally mounted on said horizontal member for movement about a single axis medially of said positioning plate and dental arches and above the posterior portion of the upper palate beyond the open end of the dental arches, said source of X-rays adapted to execute incremental discontinuous movements in an arcuate path behind the head of the patient and to direct the X-rays projected from said source at the approximate level of said occlusal plane from behind the patient towards separate sectionalized portions of the photographic plate in front of the patient, f. guide means on said plate holder assembly for permitting incremental lateral movement of said photographic plate in a horizontal direction relative to said fixed positioning plate, and g. means for manually shifting the angular position of said fixator device relative to said fixed positioning plate in said successive increments, to project the X-rays emanating from said source to said sectionalized portions of the photographic plate which are adapted to be successively exposed thereto.
 2. An apparatus as set forth in claim 1, wherein said plate holder assembly is generally arch-shaped in horizontal cross section for supporting the photographic plate vertically in an arch corresponding to the assembly, for recording thereon, in adjacent relation, the posterior left, the anterior left, the anterior right and posterior right exposures of the dental arches, said exposures being in slightly overlapping relation.
 3. An apparatus as set forth in claim 2, wherein said arch-shaped plate holder assembly has a vertical median adapted to be shifted laterally relative to the midsagittal plane of the dental arches during the exposure of the anterior and posterior portions of the latter on each side of said axis.
 4. An apparatus as set forth in claim 2, wherein said plate holder assembly is adapted to be shifted to its positions as close to the areas being radiographed as possible by indexing the lateral movement of the assembly to expose the sectionalized portions of the photographic plate adjacent to the respective position of the head of the patient when the respective exposures are made.
 5. An apparatus as set forth in claim 1, wherein said plate holder assembly comprises supporting means for said positioning plate extending upwardly from the lower end of said assembly, said positioning plate and supporting means being formed of radioluscent material.
 6. An apparatus as set forth in claim 1, wherein said fixator device comprises a. an auxiliary bar having the forward part thereof pivotally connected to said horizontal member of said frame for movement in a horizontal plane, b. a downwardly extending member on the rearward part of said auxiliary bar for supporting the source of X-rays, and c. cooperating detent means on said auxiliary bar and horizontal member to fix the angular relation therebetween at predetermined positions angled relative to the midsagittal plane of the patient.
 7. An apparatus as set forth in claim 6, wherein said cooperating detent means comprises detent elements disposed at equal angles ranging from 9* to 19* from said midsagittal plane, to permit substantial avoidance of the spinal column of the patient by the beam of X-rays adapted to emanate from said X-ray source when the anterior exposures on the left and right are made.
 8. An apparatus as set forth in claim 7, wherein said detent elements are disposed at an angle of approximately 14* on each side of said midsagittal plane.
 9. An apparatus as set forth in claim 6, including means on said downwardly extending member for lowering the X-ray source slightly below the occlusal plane and tilting said source upwardly for a limited angular extent in the course of exposing the central portions of the photographic plate on each side of the vertical median thereof whereby the upper central root structures of the upper dental arch may be radiographed without interference from the bone structure of the upper palate.
 10. An apparatus as set forth in claim 9, wherein said mounting means for the X-ray source is adapted to lower said source approximately one inch and to tilt the source upwardly approximately 5*.
 11. An apparatus as set forth in claim 9, wherein said plate holder assembly for supporting the photographic plate is arch-shaped in horizontal cross section for supporting the photographic plate vertically in an arch corresponding to the assembly, and position-indexing means on said assembly for locating thE fixed sectionalized positions of the photographic plate during the successive incremental exposures of the dental arches.
 12. An apparatus as set forth in claim 7, wherein said cooperating detent means comprises detent elements disposed at equal angles ranging from 37* to 47* from said midsagittal plane, to fix the trajectory of the beam of X-rays adapted to emanate from said source when the posterior exposures of the left and right sides of the dental arches are made.
 13. An apparatus as set forth in claim 6, wherein said cooperating detent means comprises detent elements disposed at equal angles ranging from 37* to 47* from said midsagittal plane, to fix the trajectory of the beam of X-rays adapted to emanate from said source when the posterior exposures of the left and right sides of the dental arches are made.
 14. An apparatus as set forth in claim 13, wherein said detent elements are disposed at an angle of approximately 42 1/2 * on each side of said midsagittal plane.
 15. An apparatus as set forth in claim 6, including means at the junction of said auxiliary bar and downwardly extending member for shifting longitudinally the radial position of the X-ray source relative to the patient.
 16. An apparatus as set forth in claim 1, wherein said positioning plate adapted to be positioned in the mouth of the patient is arch-shaped and is canted upwardly from the anterior of the mouth to tilt the occlusal plane accordingly.
 17. An apparatus as set forth in claim 16, wherein the canting angle of the positioning plate is approximately 8*. 